Controlling inductive power transfer systems

An inductive power transfer system comprising:

• a primary unit operable to generate an electromagnetic field;
• at least one secondary device, separate from the primary unit, and adapted to couple with the field when the secondary device is in proximity to the primary unit so that power is received inductively by the secondary device from the primary unit without direct electrical conductive contacts therebetween;
• a load-measuring unit for determining information relating to a power requirement of the secondary device or devices therefrom;
• communication circuitry for receiving, in the primary unit, the power requirement of the secondary device or devices therefrom;
• power measuring circuitry;
• and
• a control unit for determining if there is a substantial difference between the measured power and the power requirement, and
• the control unit operable, following such determination of a substantial difference, to restrict or stop the inductive power supply from the primary unit.

A primary unit, for use in an inductive power transfer system that also has at least one secondary device separate from the primary unit, the primary unit comprising:

• a primary coil for generating an electromagnetic field which couples with the at least one secondary device when it is in proximity to the primary unit so that power is received inductively by the secondary device from the primary unit without direct electrical conductive contacts therebetween;
• communication circuitry for receiving information relating to a power requirement of the secondary device or devices therefrom;
• power obtaining circuitry for obtaining a power drawn from the primary unit;
• and
• a control unit for determining in dependence upon the received information a power supplied to the secondary device or, if there is more than one secondary device, a combined power supplied to the secondary devices, the control unit for determining if there is a substantial difference between the obtained power and the supplied power, and the control unit operable, following such determination of a substantial difference, to restrict or stop the inductive power supply from the primary unit.

A secondary unit, for use in an inductive power transfer system that also has a primary unit, said secondary unit comprising:

• a secondary coil adapted to couple with a field generated from said primary unit when in proximity to said primary unit so that power is received inductively by said secondary unit without direct electrical conductive contacts therebetween;
• a load-measuring unit for determining information relating to a power requirement of said secondary unit;
• and
• communication circuitry for sending said power requirement to said primary unit, wherein the primary unit includes a controller configured to determine a power supplied to said secondary unit based on said power requirement, wherein the controller is configured to determine if there is a substantial difference between a power measured in the primary unit and the power supplied, and following such determination of a substantial difference, to restrict or stop supply of inductive power from the primary unit;
• and
• said communication circuitry varying a load to communicate said power requirement to said primary unit.